T138 Glacial Lake Agassiz—Its History and Influence on North America and on Global Systems: In Honor of James T. Teller

Monday, 10 October 2011
1:30 PM - 5:30 PM
Room L100FG

"CANADIAN" RADIOGENIC ISOTOPE SIGNATURE OF YOUNGER DRYAS AGE ICE-RAFTED SEDIMENTS IN SEDIMENTARY SEQUENCES FROM LOMONOSOV RIDGE AND FRAM STRAIT

Paper number: T138-9
Program: Technical Sessions
Time: 3:20 PM – 3:35 PM

Authors

Abstract

The Younger Dryas (YD) cooling event and the related slowing of the Atlantic Meridional Overturning Circulation (AMOC) have been linked to a large array of processes. Thee most widely supported causal mechanism involves an influx of freshwater into the North Atlantic Ocean linked to a partial drainage of glacial Lake Agassiz. Recently, a northward drainage route, through the Mackenzie River outlet into the Arctic Ocean, has been suggested from land-based studies [Murton et al., Nature 464, 740-743]. Sedimentological and geochemical analysis of cores raised from Lomonosov Ridge and the Fram Strait area, yield relatively robust evidence for enhanced ice-rafting deposition -IRD- (with a 5-fold increase -) during the critical interval. At Lomonosov, the corresponding sedimentary layer (from ca. 13 to 12 ka) is marked by a pulse of detrital carbonates in the silt to sand fractions, with approximately equal amounts of calcite and dolomite, pointing towards an Arctic Canadian sediment source area. The layer also depicts a 5 fold increase 230Th-excess, which we link to an enhanced flux of scavenging particles. Here, we examine further the geochemical signatures of the YD-layer based on elemental (Zr/Al) and isotopic (Sr, Nd and Pb) data on bulk sediments and residues ensuing from the removal of exchangeable fractions (Zr/Al, Nd, Pb, Sr), thought to label detrital sediment source areas. Based on a survey of literature we broadly identify three major source areas variably contributing to IRD during the MIS 3-Present interval: the Russian, Canadian and Greenland margins. The YD interval is particularly highlighted by strong elemental and isotopic excursions, notably a peak in radiogenic Sr, indicating prominent supplies from the Canadian end-member. This suggests enhanced sea-ice production and drifting along the Beauford Gyre. A major drainage event along the Mackenzie outlet area, as proposed in the above reference, would be a suitable trigger for enhanced sea-ice production, leading to the nearly 5-fold export of Arctic sea-ice suggested by our data. As already proposed by Tarasov and Peltier [Nature 435, 662-665], such a routing of freshwater would have been very efficient in reducing the AMOC in the Greenland, Iceland and Norwegian seas, and/or in the North Atlantic area south of the Denmark, Iceland-Faroe-Scotland, sills.